Re: [PATCH/RFC 7/9] Virtual network guest device driver

Eric Van Hensbergen
2007-05-24T00:07:45Z

On 5/23/07, Eric Van Hensbergen <ericvh-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On 5/23/07, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> > On Wednesday 23 May 2007, Eric Van Hensbergen wrote:
> > > On 5/23/07, Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org> wrote:
> > > >
> > > > For me, plan9 does provide answers to a lot of above requirements.
> > > > However, it does not provide capabilities for shared memory and it
> > > > adds extra complexity. It's been designed to solve a different problem.
> > > >
> > > As a point of clarification, plan9 protocols have been used over
> > > shared memory for resource access on virtualized systems for the past
> > > 3 years. There are certainly ways it can be further optimized, but it
> > > is not a restriction.
> >
> > I think what Carsten means is to have a mmap interface over 9p, not
> > implementing 9p by means of shared memory, which is what I guess
> > you are referring to.
> >
> > If you want to share memory areas between a guest and the host
> > or another guest, you can't do that with the regular Tread/Twrite
> > interface that 9p has on a file.
> >

ugh. I'm tired. Its been a long week -- I realized after I fired off
that last message that you mean establishing a shared mapping versus
support for mmap operations over 9p (which devolve into Tread/Twrite).
Sorry. Yes -- that's correct, 9p wouldn't necessarily buy you
something like that. In fact, the current 9p code relies on someone
else providing that basic mechanism in order for us to establish our
shared memory transport.

What Carsten described as his virtual device abstraction sounded like
a good foundation -- just don't make me use ioctl :)

-eric